I might be wrong but it felt like their defence suffered the exact same way ours did in the opening 3 games, Maguire and Lindelof got no protection from midfield either and looked like pub players because of it. If you let quality attackers run at defenders over and over again, no matter who the defender is the attacker will get the best of them eventually and if you get the beating of a CB that usually results in a 1 on 1 with a keeper.
It felt that way because it was progressive. It reminded me the Spurs game and in fact Upamecano's game was similar to Maguire's where he tried to force things in the last third and wasn't in place when the attack unsurprisingly failed. People focus too much on individuals, in both cases while the players made mistakes those mistakes were the fruit of poor team organization and in the case of Leipzig a subpar attacking force.
I know that many posters don't want to accept that fact but United have very good players and should be a Top 10 team in Europe, our issues are due to punctual poor coaching which is shown everytime Ole decides to take logical decisions/actions, thats when we can see that the coaching staff can implement good tactical plans and that the players are able to execute them. In the case of Leipzig it was a similar problem, as
@RedSky mentioned things got worse with every boneheaded decisions that Nagelsmann took, he is a very coach because his teams isn't as talented as their regular level would make you believe but when he fails to concoct the perfect plan you can see how they completely implode and their back three was totally exposed for the entirety of the game.
Also the way Ole organized the attack meant that we stretched their back three with both strikers starting outside of the RCB and LCBs while Van De Beek played almost like a false nine and occupied the CB, it meant that our attackers were never doubled without leaving an other attacker completely free and since Leipzig wingbacks weren't tracking deep or covering inside.
On a side note that game is a case for a flat midfield three and switching between a 433 and 4312. I wanted to see it for a while and it's convincing.